ci: align job counts across CI providers

GitHub Actions sets JOBS to ten regardless of runner size, while
GitLab CI uses the detected CPU count. Use the CPU count for Make and
prove on both providers, selecting JOBS after the operating system
is identified.

Use nproc on Linux and NUMBER_OF_PROCESSORS on Windows. On macOS, use
sysctl to avoid requiring nproc before the dependency installer has run;
GitHub macOS images need not provide GNU coreutils.

Assisted-by: LLM
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

ci/lib.sh

@@ -226,7 +226,6 @@ then
 	cache_dir="$HOME/none"
 
 	GIT_TEST_OPTS="--github-workflow-markup"
-	JOBS=10
 
 	distro=$(echo "$CI_JOB_IMAGE" | tr : -)
 elif test true = "$GITLAB_CI"
@@ -242,7 +241,6 @@ then
 	case "$OS,$CI_JOB_IMAGE" in
 	Windows_NT,*)
 		CI_OS_NAME=windows
-		JOBS=$NUMBER_OF_PROCESSORS
 		;;
 	*,macos-*)
 		# GitLab CI has Python installed via multiple package managers,
@@ -252,11 +250,9 @@ then
 		export PATH="$(brew --prefix)/bin:$PATH"
 
 		CI_OS_NAME=osx
-		JOBS=$(nproc)
 		;;
 	*,almalinux:*|*,alpine:*|*,debian:*|*,fedora:*|*,ubuntu:*|*,i386/ubuntu:*)
 		CI_OS_NAME=linux
-		JOBS=$(nproc)
 		;;
 	*)
 		echo "Could not identify OS image" >&2
@@ -283,6 +279,18 @@ else
 	exit 1
 fi
 
+case "$CI_OS_NAME" in
+windows|windows_nt)
+	JOBS=$NUMBER_OF_PROCESSORS
+	;;
+osx)
+	JOBS=$(sysctl -n hw.logicalcpu)
+	;;
+*)
+	JOBS=$(nproc)
+	;;
+esac
+
 MAKEFLAGS="$MAKEFLAGS --jobs=$JOBS"
 GIT_PROVE_OPTS="--timer --jobs $JOBS"